Transmit-receive device



2 Sheets-Sheet 1 Filed Aug. 5, 1945 RECEIVER TRANSMITTER R W C 7 T H 3 C 3 1+. E Q P R 6 2 6 3 2 y r5 3 m A u m E T N A awe/MM BRUCE a. CORK radio transmitter and the radio receiver.

Patented Sept. 19, 1950 UNITED STATES PATENT OFFICE TRANSMIT-RECEIVE DEVICE Bruce B. Cork, Peck, Mich., .assignor, 'by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application August 3, 1945, Serial No. 608,696

6 Claims. (01. 178-44) This invention relates to. a transmit-receive device comprising a pair of resonant circuit means so coupled that a broad band frequency response is obtained. More particularl this invention relates to a pair of resonant transmission line sections having an energy coupling means there between which is eiTective to produce a broad pass band for energy of fundamental frequency while discriminating against passage of an undesired harmonic.

In connection with radiant energ direction finding, ranging, and identification devices, it is known to employ a common antenna for both the Such dual use is made possible by the employment of a transmit-receive device, more commonly known as a TR. A customary form of TB is one which serves to block passage of energy to the receiver during the period thatthe transmitter is energized and to allow the receiver to be coupled to the antenna during that portion of th operating cycle when the transmitter is not energized. One type of widely used TR for .accomplishing this result consists of a non-linea impedance interposed between the receiver and the antenna which changes in magnitude abruptly upon reception of the initial transmitted pulse, thereby introducing a mismatch in the circuit between the antenna and receiver. Upon cessation of transmission, the TR restores itself to normalcy, passing to the receiver any energy received by the antenna.

It isan object of this invention to produce an improved TR device which will function more effectively than have devices of the prior art to produce the desired receiver protection.

It is another object of this invention to produce an energy translating device capable of passing only a desired band of frequencies while discriminating against an undesired harmonic.

It is another object of this invention to produce a TR. which will have frequency discriminating properties such that a fairly wide band of frequencies lying in the range which it is desired to receive will be satisfactorily translated to the receiver.

It is a further object of this invention to produce a TR which will have a Wide, fiat frequency response curve, and which will be capable of substantiall blocking translation of a given undesired harmonic frequency.

In accordance with these objects this invention will now be described wi h reference to the accompanying drawings, in which:

Fig. 1 shows schematically the operation of a transmit-receive, or TR, device in connection with 2 a transmitter and receiver employing a common antenna;

Fig. 2 illustrates in cross section an elevation of One embodiment of this invention, taken along line 2-2 of Fig. 3;

Fig. 3 illustrates a cross sectional plan of the same embodiment of this invention taken along line 3-3 of Fig. 2;

Fig. l illustrates schematically the operation of the device of Figs. 2 and 3 in response to energy of fundamental frequency;

Fig. 5 illustrates schematically the operation of the device of Figs. 2 and 3 in response to energy of an undesired harmonic, in this case the third harmonic; and

Fig. 6 illustrates an alternative form of con struction for a portion Of the device illustrated in Fig. 2.

Referring noW to the schematic diagram of Fig. i, there is shown an antenna i0 serving both a transmitter H and a receiver (2. Interposed between receiver l2 and antenna 10 is a transmitreceive, or TR, device l3. As explained hereinbefore, the function of TRIB is to protect receiver l2 from the high level energy introduced into the antenna when transmitter l l is energized. When transmitter II is not energized, it is the function of TR|3 to translate from antenna It to receiver l2 energy of a desired frequenc or frequencies.

Referring now to Figs. 2 and 3, one embcdiment of 2. TR as illustrated schematically at I3 in Fig. 1, and embodying the principles of this invention isshown.

The TR consists of a pair of resonant, energytranslating devices in the form of cavities 29 and 2!, having a common wall 22. In the particular embodiment shown, the resonant cavities Eli and 21 comprise quarter-wave concentric transmission line sections consisting of inne conductors 23 and 24, respectively, and outer conductors 25 and 25, respectively. The concentric transmission line sections thus described are one quarter wave length AA) long at the fundamental frequencytc be translated; are short circuited at one end by conducting closure members 21? and 28, respectively; and are open circuited at their opposite respective ends, where inner conductors and 24 terminate at 3! and 32, respectively. The cavity is closed b flexible discs 29 and 3!], the movement of which tunes the cavities by virtue of the change in capacity produced between conductors 2'3 and 45, and 24 and 46.

Energy, predominantly of the fundamental frequency to which the cavities 20 and ii are tuned, is introduced into cavity 2i! by means of input coupling loop 33 fed by coaxial transmission line 34, which, as illustrated in Fig. l, is connected to antenna H]. In wall 22, common to both cavities 20 and 2|, an energy translating opening 35 is cut, forming iris coupling between the transmission line sections. Output energy is derived from resonant cavity 2| by a coupling loop 36 feeding a coaxial transmission line 31, which, as illustrated in Fig. l, is connected to the receiver of the system.

The device thus far described constitutes a pair 01" tuned resonant circuits coupled together so that energy is transferred therebetween. The coupling k, determined by the size and shape of iris 35, may be 50 chosen that a fairly wide and fiat pass band characteristic, having a midpoint frequency equal to the resonant frequency to which the two cavities are tuned, is provided.

As thus described, the TR serves to translate from the antenna to the receiver all frequencies lying within its pass band characteristic.

The protective feature of the TR is provided by a TR tube 4|! consisting of a sealed, nonconductive envelope 4| filled with a suitable gaseous medium. Tube 46 contains a pair of electrodes, the first in the form of an open ended cylinder 42 surrounding a second elongated terminal 43 insulated therefrom by suitable insulating material 44. A direct voltage is applied continuously between terminals 42 and 43 to maintain the required minimum ionization of the gas within tube 40. This continuous minimum ionization is not sufficient to form a substantially conducting path between end 3| of inner conductor 23 and the extension of inner conductor 23 formed by the short cylinder 45. Therefore, in the absence of changed conditions within tube 40, transmission line 23-25 will be substantially open circuited at end 3| thereof. With the application of increased potential between end 3| of conductor 23 and conductor 45, the gas within tube 40, already in a state of ionization, will be much more ionized; and a substantially conducting path will be formed within tube 40 by virtue of the ionization of the gas therein. This will change the dielectric properties of the path between conductors 23 and 45 to such an extent that a low impedance path will be provided for high frequency energy. This will substantially short circuit end 3| of inner conductor 23, causing resonant cavity to be equivalent to a quarter-wave transmission line section short circuited at both ends.

The operation of the TR device is as follows. When transmitter II is not operating, energy passes from antenna ill through coaxial line 34 into resonant cavity 20. Thence it is coupled through iris 35 into resonant cavity 2|, from which it is applied to receiver l2 through loop 36 and coaxial line 31. During this part of the cycle the TR device serves as a double tuned resonant coupling means.

Upon energization of transmitter high level energy enters cavity 2|] causing a greatly increased potential to appear between end 3| of conductor 23 and conductor 45. Ionization with tube 40 suddenly increases, greatly decreasing the impedance between conductors 23 and and substantially short circuiting the transmission line section. The section is thus no longer resonant at the incoming frequency and hence the energy existing therein is decreased greatly and only a small amount is coupled through iris 35 into cavity 2|. If such energy as is coupled into cavity 2| exceeds the safe value for receiver 2|, the gas within tube 50, corresponding to tube 40, increases greatly in ionization and a similar detuning of cavity 2| takes place. For many applications, tube 4|] provides adequate protection, and tube is used only to provide circuit balance between the two tuned circuits.

As has been mentioned, iris 35 serves to couple energy between cavity 20 and cavity 2 A feature of this invention involves the placing of iris 35 in such a position that energy of fundamental frequency, i. e., that for which the concentric lines 2325 and 24-26 are electrically a quarter-wave long, is satisfactorily coupled, while energy of an undesired harmonic frequency is substantially blocked.

Reference to Fig. 4 and to Fig. 5 will illustrate the manner in which iris 35 serves to couple energy of fundamental frequency while blocking coupling of energy of an undesired harmonic, in this case the third harmonic.

Fig. 4 illustrates schematically the coupling for the fundamental. Arrowed lines represent electrostatic lines of force, an increasing electric field being indicated by increasing density of lines 6|]. Circles 6| having dots or crosses indicate magnetic lines of force in the conventional manner.

In accordance with this invention, iris 35 is disposed one-third of the electrical distance from either the short circuited or the open circuited end of the transmission line. In Figs. 4 and 5, iris 35 has been shown located one-third of the electrical length of the line away from the short circuited end.

For the fundamental, illustrated in Fig. 4, electrostatic lines of force 62 and 63 pass through iris 35 and terminate on the inner conductor 24 of cavity 2|. Likewise magnetic lines of force penetrate the iris and exist in cavity 2|, where they are shown as flux lines entering the plane of the drawing. For both electrostatic lines 62 and 63 the Poynting vectors, EXT-l, representing the direction of energy flow, are in the same direction so that a net energy transfer takes place between cavities 20 and 2|.

Fig. 5 illustrates how iris 35 substantially blocks transmission of energy of third harmonic frequency cavities 2B and 2|. For the third harmonic, three quarter-waves exist instead of the single quarter-Wave shown in Fig. 4. At the iris 35 the electrostatic lines will be maximum and in a common direction, as illustrated by lines 10. However, at a point opposite the center of iris 35, the direction of the electromagnetic lines of force will reverse, as shown by the opposite polarities in the circles H and 52. Therefore, the Poynting vector, EXH, obtained by the interaction of magnetic line H and the associated electric line it is to the left, while the Poynting vector for magnetic line 12 is to the right. The iris will thus couple a net energy of zero at the third harmonic frequency.

It is to be understood that Figs. 4 and 5 are schematic only and field distortions due to physical discontinuities and to the iris itself have been neglected. Such effects will require that certain empirical tests be made to determine the exact optimum placement of iris 35.

As mentioned hereinbefore, for certain applicati0ns,TR tube 50 connected across transmission line section 2426, corresponding to tube 40 in line 23-25. serves simply to balance electrically the pair of tuned circuits. Accordingly, for such use it may be replaced by a corresponding capacitive member. In Fig. 6, TR tube 50 has been replaced. by an adjustable screw member 15, which may be adjusted so that the transmission line section 24-16 is tuned to exactly the same frequency as transmission line 23-25 containing TR tube 40.

It is not necessary in practicing this invention that any particular type of coupling be used. In the particular embodiment illustrated, the input coupling and output coupling have been shown as inductive, in the form of loops 33 and 36, respectively; while coupling between tuned circuits has been shown as iris coupling represented by opening 35. If desired, inductive, capacitive,

or iris coupling may be used for any or all of the necessary coupling functions. v

It will be apparent that while there has been shown a coupling means which substantially rejects the third harmonic, energy of any undesired harmonic frequency may be discriminated against by proper disposition of the coupling means.

From the above description it will be seen that there has been described a double tuned TR device in which the band pass characteristic may be varied in accordance with the degree of coupling between the two tuned circuits, and which substantially impedes translation of an undesired harmonic by proper placement of the coupling means.

Although I have shown and described certain specific embodiments of the invention, I am fully aware of the many modifications possible thereof. This invention is not to be restricted except insofar as is necessitated by prior art and the spirit of the appended claims.

What is claimed is:

1. Energy translating means comprising a plurality of conducting walls forming a pair of cavities resonant at a fundamental frequency, one of said walls being common to said cavities, coupling means in a wall of one of said cavities for applying energy thereto, coupling means in a wall of the other of said cavities for deriving energy therefrom, and iris coupling means positioned in said common wall at a point thereon where there is a reversal in standing wave polarity of one of the energy fields of an undesired harmonic.

2. A transmit-receive device comprising a first concentric transmission line section, a second concentric transmission line section, said sections being resonant at a fundamental frequency and having a conducting member common to the outer conductors of said sections, means for applying energy to said first section, means for deriving energy from said second section, iris coupling means positioned in said common wall at a point therein where the vector representing the standing wave pattern of energy flow for an undesired harmonic reverses in direction, and a non-linear impedance connected between inner and outer conductors of one of said sections effective to change abruptly in impedance value upon application of high voltage energy to said one circuit thereby to render non-resonant said section.

8. A transmit-receive device comprising a first concentric transmission line section resonant at a fundamental frequency, a second transmission line section resonant at said fundamental frequency. a conducting member forming a common wall between said transmission line sections, coupling means positioned in said wall at a point where there occurs phase reversal in the standing wave pattern of an energy field of a harmonic frequency to be rejected, and a non-linear impedance positioned between conductors of one of said sections effective to change abruptly in impedance value upon application of a high voltage between the conductors of said one section thereby to detune said one section from resonance. 1 4. Energy translating means comprising a plurality of conducting walls ,forming a pair of elongated cavities resonant at. a fundamental frequency and having a length equal to onefourth wavelength, one of said walls being common to said cavities, coupling means in a wall of one of said cavities for applying energy thereto, coupling means in a wall of the other of said cavities for deriving energy therefrom, and iris coupling means positioned in said common wall at a point thereon substantially one-third of the length of the cavities from an end thereof, the point being where there is a reversal in standing wave polarity of one of the energy fields of the third harmonic.

5. A transmit-receive device receptive at different times to high Power and low power pulses of electromagnetic energy, comprising: two cavity resonators the outer conductor of one resonator being in contact with the outer conductor of the other resonator, the contacting surfaces of the resonators having an iris to provide complication thereto of a high power pulse.

BRUCE B. CORK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,239,905 Trevor Apr. 29, 1941 2,340,429 Rankin Feb. 1, 1944 

